There is no lack of proposals in the prior art on how a device for deblocking spectacle lenses can be constructed, wherein use is made of a pressure medium such as water in order to release the spectacle lens from the block piece by application of hydraulic forces and, in particular, either from “inside” by way of a pressure-medium channel in the block piece, which opens at the blocking surface of the block piece facing the spectacle lens (for example, DE 10 2005 038 063 A1, FIG. 12; WO 03/018253 A1, FIG. 4), or from the “outside” by a high-pressure water jet which is delivered by a nozzle and which is incident on an edge location between block piece and spectacle lens (for example, WO 2008/003805 A1, FIG. 1).
A disadvantage of the “inside” application of the hydraulic forces is that the block piece is provided with cavities which are open towards the blocking surface and which oppose a desirable whole-area support of the spectacle lens on the block piece. The opening in the blocking surface can in principle be reduced in size in order to achieve an approximately whole-area support, but then it is hardly possible to apply the hydraulic forces required in order to separate the spectacle lens from the block piece.
The use here of a small piston in the (separate) block piece, which bounds the blocking surface, as proposed as an alternative in WO 03/018253 A1 (FIGS. 14 to 22), can admittedly be of assistance. However, mechanical forces are then applied by way of this piston during the deblocking to a relatively small, central area at the spectacle lens, which can have the consequence of destroying the spectacle lens. In any event, for the detaching it is necessary to generate forces which are higher than the adhesion forces between spectacle lens and block piece. In the case of the above-described piston solution the releasing forces act exclusively axially on the center of the spectacle lens, whereas the adhesion forces act predominantly in an annular zone at the spectacle lens edge. This can lead, particularly in the case of thin spectacle lenses, to comparatively strong deformations and high stresses in the spectacle lens to be deblocked, which ultimately can produce breakage of the spectacle lens, never mind the cost involved in providing such a piston in the block piece.
The previously known “outside” solution according to WO 2008/003805 A1, does indeed make possible a whole-area support of the spectacle lens at the block piece and beyond that reduces the risk of damage of the spectacle lens during deblocking, but this prior art is in need of improvement in another respect.
The deblocking method disclosed there was developed specifically for the deblocking of spectacle lenses blocked by a thermoplastic blocking material. In that case, melting of the blocking material is initially constrained by immersion of the composite of spectacle lens, blocking material and block piece in a bath with hot water. Block piece and blocking material as well as a protective film on the spectacle lens are then detached from the spectacle lens by a high-pressure water jet. For this purpose the water of the jet is heated to a temperature between 50° C. and 65° C. so as to further soften the blocking material and ultimately liquefy it a consequence of the heating. The high-pressure water jet is here fanned relatively widely and is, in addition, rotated about the longitudinal axis of the nozzle in order to also penetrate under the protective foil on the rotating spectacle lens and lift the blocking material and foil off the spectacle lens.
A disadvantage of this prior art can be seen particularly in that—as a consequence of the interposed pre-heating step in the hot water bath—the deblocking of a spectacle lens lasts for a relatively a long time, which is contrary to efficient use of this method in RX workshops. Moreover, this temperature-assisted method would be disadvantageous in connection with blocking methods in which use is made of non-thermoplastic blocking materials.
Finally, in the older German Patent Application 10 2009 048 590.2-14 of the same applicant a deblocking device of the “outside” type is described in which a high-pressure jet of pressure medium delivered by a nozzle is directed in the manner of CNC technology onto a predetermined point of incidence in the edge region between spectacle lens and block piece, namely through positional regulation of motor-driven movement axes, which produces a relative movement between the nozzle and blocked spectacle lens. The equipment outlay connected therewith is not, however, insignificant, so that this deblocking device is primarily suitable for larger RX workshops with a high level of automation. However, there is also a need in smaller RX workshops with a low level of automation for a device-assisted deblocking of spectacle lenses.
What is desired is a device of simplest possible construction for deblocking optical workpieces, particularly spectacle lenses, by which the optical workpieces can be deblocked as securely, free of damage and rapidly as possible.